fix: correct THRESHOLD_DEFAULTS metric keys and add missing defaults

- Rename memory_monitor threshold key from 'percent' to 'memory_percent'
  so it matches exactly rather than relying on suffix stripping, which was
  causing swap_percent to be evaluated against the memory threshold
- Add swap_percent default thresholds (warning: 40%, critical: 75%)
- Add zfs_monitor pool capacity default thresholds (warning: 80%, critical: 90%)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hbd/server/config.py

@@ -79,9 +79,13 @@ THRESHOLD_DEFAULTS = {
                 }
             },
             'memory_monitor': {
-                'percent': {
+                'memory_percent': {
                     'warning': 85.0,
                     'critical': 95.0
+                },
+                'swap_percent': {
+                    'warning': 40.0,
+                    'critical': 75.0
                 }
             },
             'disk_monitor': {
@@ -114,6 +118,10 @@ THRESHOLD_DEFAULTS = {
                             'operator': '>',
                             'hysteresis': 0.0,
                             'display': 'ZFS pool {pool_name} is {health}'
+                        },
+                        'capacity': {
+                            'warning': 80.0,
+                            'critical': 90.0,
                         }
                     }
                 }